The formation water present in subterranean geologic formations of oil, coal, and other carbonaceous materials is normally considered an obstacle to the recovery of materials from those formations. In coal mining, for example, formation water often has to be pumped out of the formation and into remote ponds to make the coal accessible to mining equipment. Similarly, formation water has to be separated from the crude oil extracted from a subterranean field and disposed of typically underground. The extraction, separation and disposal of the formation water add costs to recovery processes, and generate a by-product regarded as having little value.
Further investigation, however, has revealed that even extracted formation water can support active communities of microorganisms from the formation. The presence of these microorganism in the formation environment were known from previous recovery applications, such as microbially enhanced oil recovery (MEOR), where the microorganisms naturally generate surface active agents, such as glycolipids, that help release oil trapped in porous substrates. In MEOR applications, however, it was generally believed that the microorganisms were concentrated in a boundary layer between the oil and water phases. The bulk formation water was believed to be relatively unpopulated, because it lacked a hydrocarbon food source for the microorganisms. More recent studies have shown that robust populations of microorganisms do exist in the bulk formation water, and can even survive extraction from the geologic formation under proper conditions.
The general concept of enhancing production of biogenic methane from a carbonaceous formation has been suggested previously [Raabe, S., Denver Post, Nov. 17, 2004, p. 1C]. Volkwein, supra, reported isolating a methanogenic sediment from an abandoned coal mine into which sewage had been discharged for an unspecified time period. For mine cavities having a particular history, from a time where a nutrient source was present to a time where the nutrient source was absent, sediment could be collected which was alleged to be methanogenic in the presence of bituminous coal. No supporting data were disclosed. Scott, et al. Pub. No. US 200410033557 A1 (Feb. 19, 2004) generally describes introducing subsurface fractures in a deposit of coal, carbonaceous shale or organic-rich shale and injecting various modifications including a consortium of selected anaerobic biological microorganisms, nutrients, carbon dioxide and other substrates for in sifu conversion of organic compounds in said formation into methane and other compounds. The disclosure does not specifically teach how to obtain “selected” bacterial consortia; however, the reference suggests that collection of bacteria from formation waters may result in collection of only a few species rather than a representative sample of bacterial consortia. No supporting data of methane generation were reported. Menger, et al. U.S. Pat. No. 4,845,034 described carrying out a biochemical reaction in a subterranean cavity formed in a salt formation, limestone cavity or other earthen rock or sandstone formation. A feedstock of finely-divided, hot-alkali-treated coal would be inoculated under controlled conditions with a culture of microorganisms including acid formers and methanogens to produce methane. No data reporting methane biosynthesis were reported.
The discovery of active populations of microorganisms in bulk formation water has come at a time when new applications are being envisioned for these microorganisms. For years, energy producers have seen evidence that materials like methane are being produced biogenically in formations, presumably by microorganisms metabolizing carbonaceous substrates. Until recently, these observations have been little more than an academic curiosity, as commercial production efforts have focused mainly on the recovery of coal, oil, and other fossil fuels. However, as supplies of easily recoverable natural gas and oil continue to dwindle, and interest grows using more environmentally friendly fuels like hydrogen and methane, biogenic production methods for producing these fuels are starting to receive increased attention.
Many studies report isolating and characterizing MO's in naturally-occurring waters including ground water. Pickup et al. [Pickup, R. W. et al. (2001) J. Confam. Hydrol. %:269-2841 reported a detailed study of MO's in an aquifer polluted by a plume of phenolic material emanated from a single known source. Water from the aquifer was sampled at several depths from two boreholes within the plume. Details of the sampling method were disclosed by Thornton et al. [Thornton, S. F. et al. (2001) J, Contam. Hydrol. %:233-2671. Water samples were filtered though 0.22 pm polycarbonate filters, assayed for total MO count by acridine orange staining and by counting colonies of culturable MO's. The number of culturable MO's was 1% or less of the total measured by acridine orange staining. The authors used a variety of techniques to assess numbers and activities of various MO classes and to evaluate differences that varied with sample depth and phenolic concentration. The presence of methanogens was revealed using polymerase chain reaction analyses to amplify known methanogen-specific sequences. Methane generation was not reported.
Various filtration techniques have been reported for collecting MO's from groundwater. Schulz-Makuch et al [Schulze-Makuch, D. et al. (2003) Ground Water Monitor. and Remed. a:68-751 compared the efficacy of filter packs containing surfactant-modified zeolite or iron oxide-coated sand for removing E. coli and MS-2 virus from contaminated groundwater. The surfactant-modified zeolite removed both the bacteria and the virus, but the iron oxide-coated sand was ineffective. Lillis et al [Lillis, T. O. et al. (2001) Lett. Appl. Microbiol. 2:268-2721 compared membrane filters to collect MO's from groundwater. Recovery was measured by comparing colony counts of MO's cultured after filtration. Filters of pore size 0.45 pm recovered about 90% of the MO's; however, the remaining MO's were recovered only after filtration through 0.22 pm filters. Filtration can remove both viable and non-viable cells. Culture conditions may not be suitable for growing many, or even most of the filterable MO's. Kunicka-Goldfinger et al. (1977) Acta Microbiol. Polonica 26: 199-205, reported that an agar plate method of counting colony forming units (cfu) accounted for only 20-25% of organisms counted by direct staining of MO's isolated by filtration from lake waters. A “semi-continuous” method of culturing cells on the filters, wherein the cells were periodically exposed to filtered lake water to re-supply natural nutrients and remove waste products yielded significantly higher numbers of culturable microorganisms.
Tangential filtration has been reported for isolation of proteins and microorganisms. U.S. patent application Ser. No. 10/703,150, published Jun. 24, 2004 disclosed concentrating a suspension of microalgae by passing the suspension through a tangential filtering device. EPA document 815-0-03-008, June 2003 provides extensive technical and performance data for membrane filtration, including tangential flow filtration, in water purification systems.
To date, most contributions to the art have emphasized nutritional amendments in situ, or culturing microorganisms prior to injection into a formation or introducing fractures in a formation. Techniques for isolating a methanogenic consortium and demonstrating methanogenesis from an isolated consortium remain as problems inadequately addressed in the prior art.
Unfortunately, the techniques and infrastructure that have been developed over the past century for energy production (e.g., oil and gas drilling, coal mining, etc.) may not be easily adaptable to commercial-scale, biogenic fuel production. Conventional methods and systems for extracting formation water from a subterranean formation have focused on getting the water out quickly, and at the lowest cost. Little consideration has been given to extracting the water in ways that preserve the microorganisms living in the water. Similarly, there has been little development of methods and systems to harness microbially active formation water for enhancing biogenic production of hydrogen, methane, and other metabolic products of the microbial digestion of carbonaceous substrates. Thus, there is a need for new methods and systems of extracting, treating, and transporting formation water within, between, and/or back into geologic formations, such that microbial activity in the water can be preserved and even enhanced.
New techniques are also needed for stimulating microorganisms to produce more biogenic gases. Native consortia of hydrocarbon consuming microorganisms usually include many different species that can employ many different metabolic pathways. If the environment of a consortium is changed in the right way, it may be possible to change the relative populations of the consortium members to favor more combustible gas production. It may also be possible to influence the preferred metabolic pathways of the consortium members to favor combustible gases as the metabolic end products. Thus, there is also a need for processes that can change a formation environment to stimulate a consortium of microorganisms to produce more combustible biogenic gases.